We recently had the ball valve at the wall replaced, the plumber installed a 1/4 turn valve which is supposed to close/open with a 1/4 turn. He also installed a new fill tower for us. My wife has pointed out that flushes have been inconsistent.

My wife says that when solids are flushed, the toilet almost overflows. The water level rises to just below the lip (about 1/2" below). Sometimes a little bit of toilet paper comes back up too.
I researched this and found a test for clogs:
Pour two 5 gallon buckets in the bowl as quickly as possible. I did this and everything drained well, no overflow. The toilet seemed to handle it well.

Does anyone have any other ideas? Is there any way the fill tower could cause an issue related to the water level during a flush? The toilet fills to it's old level, albeit more slowly than before.

I don't want to call the plumber back in again, because it took him 3 trips to get the new ball valve to stop working.

Was this a problem before or is this new. It sounds to me like a plug up or no air behind water in the main drain.Strange!! I think I would look at the bowl some more.
Buy a new wax ring before you pull it off, if you do

Sounds like a clogged vent line to me.
Sometimes when a toilet back up some trash gets pushed up the vent line and starts to stop it up. If the vent is plugged it creates a vacuum in the drain line stopping the flow.

Sounds like something obstructing the vent. It probably has nothing to do with the recent repair, just sheer coincidence. Then again during the repair, debris could have been knocked loose and found it's way to create a blockage.

New information: Every time we flush (or use the plunger), we hear a running water sound for a few seconds (sounds like it is coming from somewhere else in the house). It is not coming from the toilet. Almost like there is a water supply getting turned on for 2-3 seconds. I wonder if it is our other toilet on that floor?

Thanks : Every time we flush (or use the plunger), we hear a running water sound for a few seconds (sounds like it is coming from somewhere else in the house). It is not coming from the toilet. Almost like there is a water supply getting turned on for 2-3 seconds. I wonder if it is our other toilet on that floor? w

Water hammer from this toilet could be causing the other toilet to run some more and "top off" its tank.

A cloged vent line will cause it to not flush down all the time, may only do it once in a while, will suck water out of traps and the other toilet trying to suck air. Take a straw and put your finger over the end it and suck and see how well it works.